1. Field of the Invention
The present invention relates to generally to fuel delivery systems, and more particularly, to a method of determining wall wetting for a port injected internal combustion engine.
2. Background and Summary of the Invention
Internal combustion engines are employed most efficiently and with minimal pollution when the correct fuel to air ratio is maintained. This is easier said than done, because transient conditions during engine operation make it difficult to determine the precise quantity of fuel that should be injected at any given instant. In a present-day fuel injection system, fuel is injected into the intake port of the fuel intake manifold. There, the fuel is mixed with air and introduced into the cylinder when the intake valve is opened. There are several factors which contribute to the efficient delivery of the fuel droplets into the cylinder. These factors include the injector targeting which includes the direction of fuel spray from the injector relative to the intake valve. Another factor is the injection timing which involves the start and finish times for injecting fuel relative to the times that the valve is opened and closed. The injection spray envelope is also an important factor in reducing wall wetting. An injection spray envelope which is too narrow causes a fuel droplet spray which does not properly mix with the air being induced. An injection spray envelope which is too wide causes fuel droplets to impinge against the walls of the intake manifold, thereby causing a film to develop on the wall. The droplet size of the injected fuel is also an important factor in wall wetting. For example, if the droplets are too large, they fail to mix properly with the induced air. Since the amount of wall wetting can have a great impact on the engine emissions and performance, a simple technique for quantifying or qualifying wall wetting would be welcome during the engine development process. Thus, the optimization of injector targeting, injection timing, injection spray envelope, and injection fuel droplet size can be obtained in order to reduce the engine emissions.
Accordingly, the present invention provides a method of determining wall wetting for an engine, which includes running a multi-cylinder (or single cylinder) engine at a predetermined speed and load. The fuel delivery and spark to one of the cylinders is then interrupted. The hydrocarbon level exhausted from the cylinder is then measured for a predetermined number of engine cycles. The test results can then be curve fitted to the relationship HCPPM=(A+BN).sup.(1/exp). In this relationship, HCPPM is the hydrocarbon count in parts per million, A and B are each constants, N is the number of engine cycles after interrupt and the exponent "exp" is derived using an iterative process. The exponent which is derived is the main qualifier for wall wetting.
The apparatus for determining wall wetting for an engine according to the present invention includes a dynamometer attached to an output of the engine. A hydrocarbon level detector disposed in an exhaust passage of a cylinder of the engine. A fuel delivery and spark interrupting device is provided for interrupting fuel delivery and spark to the cylinder of the engine. A crank angle data acquisition device is provided for counting engine cycles of the engine. A processor is provided for curve fitting data obtained by the hydrocarbon level detector and the fuel delivery and spark interrupting device to the relationship HCPPM=(A+BN).sup.(1/exp) and solving for the exponent exp.
The method of the present invention can be utilized for comparing different injector targeting, injection timing, injection spray envelope, and injected fuel droplet size set up arrangements. Thus, the method of the present invention provides a simple technique for optimization of each of these factors.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.